spark plug thread fix

[78XS400]

yo guys, need a bit of advice on the best way way to fix my spark plug threads. the plug goes in like halfway, then starts to tighten, but never fully tightens, just turns.

should i run a thread chaser thru it? tap it? helicoil?

and my followup question, whats the best way to prevent whatever metal shavings that u get, from falling into the cylinder?

[Sev]

You're going to need to helicoil it. If you can flip the engine upside down. If you can't do that, then apply grease to the drill bit, then the tap when you're cutting the threads. Go very slowly.

Alternately snap-on and MAC tools make specially designed thread cutters that compress, go into the hole, then expand outwards to cut the threads. They have little cups to hold the shavings, but cost about $100 each.

[ofblong]

holy expensive sev.

you sure that your spark plug ratchet isnt hitting the housing? I found that on my bike I had to actually take the 18MM spark plug bit and use my grinder to grind it down quite a ways so it wouldnt tighten down on the housing and would allow me to completly tighten down the spark plug.

[slimcolo]

Assuming that your head is aluminum, some are cast iron, a magnet will not work for chips. Best to remove head for this operation. (on my HD this takes about an hour on my BMW a lot less, mt Yamaha only has 4 bolts on head, some bikes require that you remove motor from the frame to remove head) Helicoil is very good but there are others on the market.

Locktite makes a thread repair that is a gel. It works like JB WELD but will only stick to non ferrous metals. I have never used this but have heard good reports. It can be had at most upper end auto stores. (Napa,Big A not Autozone or Checker)

[Sev]

holy expensive sev.

you sure that your spark plug ratchet isnt hitting the housing? I found that on my bike I had to actually take the 18MM spark plug bit and use my grinder to grind it down quite a ways so it wouldnt tighten down on the housing and would allow me to completly tighten down the spark plug.

Tighten, then loosen is a sign of stripped threads. And yes it's expensive, but that's because it's snap-on you're paying for the name, the tech, and the warantee.

Again, you can smear a large amount of assembly grease on the drill bit or the tap. This will make the shavings stick to it. Then you clean off and reapply as needed until you're done with your drilling/tapping.

[78XS400]

removing the head is not an option, its a 78, i don need the threads to be perfect, cuz they'll probably get messed up again in a year (air-cooled engines like to do this). i figure ill try to clean up the threads first, if that dont work, ill see how expensive a helicol is, or ill just put sum fking jbweld and retap it, and shove a bunch of locktite in it.

[slimcolo]

The Locktite I was talking about is specifically made for thread repair, It is not regular Locktite!

[78XS400]

ill shove everything in there and ill never take that plug out again, lol

[beemer_scoot]

Heli-coils are a bad fix. They'll come apart the next time you take the plug out. Your local auto parts store should have a "bushing type" spark plug repair kit. It should have everything thing you need to install a steel tube that's theaded on the inside and outside, and it crimps in place.
I installed one about a year ago in an aluminum head. I didn't remove the head either. Cover any cutting tools you use with grease to catch as many shavings as you can. Then clean out what shavings you can get to. Turn the engine over by hand to make sure nothing is left in the cylinder that do do any real damage. Start it up and rev the engine to make sure the rest of the shavings blow out.

[Sev]

I've never seen a heli-coil that was correctly installed work it's way back out. In fact some of the older British race bikes had every single mount drilled out then helicoiled because it allowed all the bolts to be installed at a higher torque rating.